[SOLVED] "%s New Plural" displayed after importing Discussions

I imported quite a lot vbulletin discussions using the vanilla-importer. And everything worked quite smoothly - but when I browse the discussions page, it shows "%s New Plural" instead of the amount of "unread" comments.

Can anyone help me on how to fix this? I would rather like to have it displayed "1" or "0". I tried digging into the code, but couldn't figure out where this is coming from...